The present invention relates to a multi-digit luminescent display tube having a plurality of pattern display sections arranged in the form of a matrix.
With the recent progress and diversification of all kinds of electronic devices, there has been an increasing need of display devices capable of displaying more kinds and greater amounts of information.
For instance, in a display device which employs a luminescent display tube characterized by its clear luminescent color, low-voltage operation, low power consumption, etc., the luminescent display tube is made to be of the so-called multi-digit type having a plurality of pattern display sections arranged in one direction so that the amount of information that can be displayed may be increased. In this case, however, if the pattern display sections increase in number, the area they require will be lengthened in the direction of their arrangement and therefore the display tube will be increased in size and as a result will become too large to be incorporated in an electronic device.
As another example, there is a luminescent display device which is provided with a plurality of multi-digit luminescent display tubes disposed parallel with each other in the direction vertical to the arrangement direction of the pattern display sections so as to increase the amount of information that can be displayed. In the case of such a luminescent display device, however, complicated connecting operations are required for the multi-digit luminescent display tubes when it is to be incorporated into an electronic device. Therefore, problems exist from the standpoint of operational efficiency or production.
Various multi-digit luminescent display tubes recently proposed in view of the above facts are of the type which has a container containing a plurality of pattern display sections arranged in the form of a matrix or in the directions of row and column so that the amount of information that can be displayed may be increased and diversified. The multi-digit luminescent display tube of this type will be hereinafter described with reference to FIG. 1 which shows a schematical plan view of the essential part thereof.
In FIG. 1, the reference numeral 1 designates a substrate made of insulating material such as glass or ceramics. A plurality of pattern display sections 2(2.sub.11, . . . , 2.sub.mn) are arranged on the substrate 1 in the form of a matrix or in the directions of row and column. Each of the pattern display sections 2 is made up of a plurality of segment anodes each having a luminescent material layer thereon. Control grids 3(3.sub.11, . . . , 3.sub.mn) are provided above and in the vicinity of the pattern display sections 2(2.sub.11, . . . , 2.sub.mn), respectively. Filament-shaped cathodes 4(4.sub.1, . . . , 4.sub.mn), which are adapted to emit thermions when heated, are stretched over the control grids 3 in the direction of, for instance, the row of the matrix of the pattern display sections 2. In addition, a box-shaped or flat-bottom-boat-shaped front bulb (though not shown) made of transparent material such as glass is bonded at its periphery to the substrate or base plate 1 so that the above-mentioned anodes, grids, cathodes and the like may be kept airtight in a vacuum. Reference numeral 5 designates external terminals connected to the above anodes, grids, cathodes and the like so as to energize them.
In the multi-digit luminescent tube constructed as above, thermions emitted from the cathodes or filaments 4 impinge on the pattern display sections 2 to excite the luminescent material thereby making it luminesce, only when the pattern display sections 2 and grids 3 are both sufficiently positive with respect to the cathodes or filaments 4. In this tube, therefore, the pattern display sections 2 corresponding to necessary digits may be selectively excited to luminesce by selectively making the corresponding pattern display sections 2 and grids 3 positive with respect to the filaments 4.
In the case of the multi-digit luminescent tube of the type mentioned above, the following driving method has been proposed to selectively excite each pattern display section 2 to make it luminesce while making the number of the external terminals 5 as small as possible.
Corresponding segment anodes of the pattern display sections 2 of all digits are electrically connected to each other, respectively. Grids 3 of each column are electrically connected to each other, being connected to the corresponding external terminal 5. The filament 4 for each row is connected to the corresponding external terminal 5 independently.
With the above-mentioned arrangement, the display signal is given to the pattern display sections 2 in which the corresponding segment anodes are connected to each other throughout all the digits; the column-selecting signal is given in a time-sharing manner to the grids 3 which are connected to each other for each column; and power for heating is given to the filament 4 provided for each row, and in addition signals are given to the filament 4 to make the potential thereof substantially negative in response to the above display signal and column-selecting signal.
Under the above-mentioned conditions, if a negative potential given to the filament 4.sub.1 provided for the first row of the matrix of the pattern display sections 2 and the first-column grids (3.sub.11, 3.sub.21, . . . , 3.sub.m1) are selected in response to the column-selecting signal, the above-mentioned requirement for luminescing will be satisfied only at the pattern display section 2.sub.11 positioned at the intersection of the first row and first column of the matrix, and therefore luminescent display is performed at the pattern display section 2.sub.11. If, then, the column-selecting signal is shifted to the second-column grids 3(3.sub.12, 3.sub.22, . . . , 3.sub.m2), the first-row second-column pattern display section 2.sub.12 will satisfy the luminescing requirements and therefore will perform luminescent display. After the luminescent display at the pattern display sections 2 on the first row is completed in this manner, the filament 4.sub.2 for the second-row pattern display sections 2(2.sub.21, 2.sub.22, . . . , 2.sub.2n) are made negative and thereby selectively performs luminescent display. In the same manner, luminescent display can be performed up to the m-th row and n-th column pattern display section 2.sub.mn. In this case, it is not necessarily required to make the pattern display sections 2 luminesce in the order mentioned above and to make the pattern display sections 2 of all digits luminesce at one display operation. In short, the pattern display sections 2 positioned at the points where the column of the grids 3 to which the column-selecting signal is given intersect with the filament 4 to which a negative potential is given.
The above-mentioned driving method can minimize the number of the external terminals 5 that must be added when the number of the pattern display sections 2 and that of the anodes of the pattern display section are increased. In addition, it permits easy production, simple driving circuits and low cost.
However, the above driving method has the following disadvantage:
As mentioned above, the first-row first-column pattern display section 2.sub.11 is selected for luminescing, when the filament 4.sub.1 for the first-row pattern display sections 2 (2.sub.11, 2.sub.12, . . . , 2.sub.1n) is at a negative potential and the first-column grids 3(3.sub.11, 3.sub.21, . . . , 3.sub.m1) are selected in response to the column-selecting signal. In this case, the second-row first-column grid 3.sub.21 is also kept at a positive potential under the influence of the column-selecting signal and the display signal is given to the pattern display sections throughout all the digits; therefore, thermions emitted from the filament 4.sub.1 tend to impinge on the unselected pattern display section 2.sub.21 under the influence of an electric field formed by the grid 3.sub.21 kept at a positive potential and thereby to excite it for luminescing. In short, there is a possibility that the above-driving method is accompanied by leakage luminescence occurring at the pattern display sections 2 on the unselected row.